Composites that have incorporated therein filler material comprised of carbonaceous nano-scaled materials, such as carbon nanotubes and graphene, have held great promise due to the superior electrical and mechanical properties of such materials. However, the hoped for results have seldom been realized. As an example, while moderate increases in stiffness have been achieved, the strength and strain to failure of the matrix are usually degraded. The disappointing performance has been attributed to the inadequate wettability of the filler material's surface as well as the poor dispersion of the carbonaceous filler material throughout the matrix.
Various processing remedies have been explored, including ultrasonication, chemical acid treatments, fluorination, amine-functionalization and oxygen vacuum plasma treatment, but have yielded limited success. The primary mechanism for most of these treatments is to incorporate oxygen containing groups on the surface of the material in order to modify the surface energetics and wetting in an effort to improve distribution within a matrix. However, such techniques have been shown to introduce defects and degrade the delicate structure of the nano-scaled reinforcement material. Not only are mechanical properties adversely affected, but damage to the outer walls of these materials has been shown to also negatively impact electrical property performance by reducing percolation pathways.
Atmospheric plasma treatment has also been explored as a means for treating the surface of a material in an effort to enhance wetting and dispersion. Such treatment is generally desirable as it requires minimal operator intervention, is performed at atmospheric pressure, can be applied to complex shapes and has been shown to modify and incorporate specific functional groups onto the surface of a hydrophobic material which results in improvements in wetting, tenacity, bond strength and fracture toughness. The treatment is typically performed using an active gas such as oxygen, nitrogen, water, ammonia or carbon dioxide. Unfortunately, even using oxygen or carbon dioxide as the active gas has been shown to be of limited utility as the degree of oxygen incorporation is minimal and even with the low degree of incorporation, damage of the graphitic structure is substantial and has been shown to negatively impact both electrical as well a mechanical performance.
A method for enhancing the wettability and dispersion of carbonaceous nano-scaled filler material in a resin matrix is therefore needed. A composite having such material incorporated therein would be expected to yield improved mechanical and electrical properties.